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RE: FWIW

Posted by morricab on May 23, 2014 at 01:44:13:
Well that is true for an OTL as long as you are not using negative feedback. You can get the same drop in distortion also with SS devices if you don't use feedback.

As for not needing single ended...I disagree with you on this one because push/pull is inherently not perfect and as such creates distortion just on the mismatch between the two pushing and pulling devices will generate additional and unnatural distortions. Also, the cancellation of even order harmonics results in a less natural harmonic progression that is not seen in nature...nature is single ended.

With phase/time coherent speakers one can hear these trait differences regardless of how good the amps are. It was particularly obvious when I was using Acoustat full range electrostats and nearly as obvious with my current Reference 3a speakers.

MOST OTLs use a fair amount of negative feedback (even your small one the S30 does if I am not mistaken), which pushes them even further from the ideal distortion pattern, so while the benefits of greater transparency and usually tighter bass are there the tonal balance is shifted sadly more towards a typical "solid state" kind of leanness. If you read the reviews of your M60 OTLs, many of the reviewers note a slight leannes to the sound. For sure much of the warmth of the SET amps is derived from the output transformer distorting; however, I think that the best ones keep a natural sounding tone without undue warmth or leanness and they are almost always without negative feedback.

I recently had on hand the very nice sounding VAC Renaissance 30/30 MKIII, which has a nice tone and very high resolution. However, I could hear that it was push/pull because some things just didn't have the coherence one gets from my SET amps. It took quite some listening to nail it down but once I did I couldn't keep the VAC. I also tried an Einstein hybrid...it sounded relatively dead compared to a good SET.

You might be interested to read about my current amplifier, the NAT Symbiosis SE

http://www.nataudio.ch/cms/index.php?page=symbiosis-se-single-ended-integrated-amplifie

It is rather unique in that it is truly single ended (only one output device per channel) but that output device is a big industrial MOSFET. THe input and driver are 9 pin small signal tubes. It is all direct coupled and zero negative feedback. There are also 2 other industrial MOSFETS acting as regulators for the output ones (that is why there are 4 big heatsink towers).

What does it sound like? A big SET without any fluff around the notes...it is very precise and very dynamic but the tone is quite natural. When it fully warms up (over 1 hour of playing) it also has that otherworldly transparency of OTL. Until then it has the transparency of a good SET. Bass is very well controlled and powerful but natural as well. It is there that one can tell the output is a transistor.

That said, I think that a true SET OTL could be even better but it would be tough to do without adding a fairly significant amount of negative feedback...or would it?? I put it to you as a challenge. I know of only one on the market from Transcendent Sound but I would have to buy monos to get a reasonable 12 watts. Still I am considering...